UV epoxy bonding for enhanced SAW transmission and microscale acoustofluidic integration

Surface acoustic waves (SAWs) are appealing as a means to manipulate fluids within lab-on-a-chip systems. However, current acoustofluidic devices almost universally rely on elastomeric materials, especially PDMS, that are inherently ill-suited for conveyance of elastic energy due to their strong attenuation properties. Here, we explore the use of a low-viscosity UV epoxy resin for room temperature bonding of lithium niobate (LiNbO(3)), the most widely used anisotropic piezoelectric substrate used in the generation of SAWs, to standard micromachined superstrates such as Pyrex? and silicon. The bonding methodology is straightforward and allows for reliable production of sub-micron bonds that are capable of enduring the high surface strains and accelerations needed for conveyance of SAWs. Devices prepared with this approach display as much as two orders of magnitude, or 20 dB, improvement in SAW transmission compared to those fabricated using the standard PDMS elastomer. This enhancement enables a broad range of applications in acoustofluidics that are consistent with the low power requirements of portable battery-driven circuits and the development of genuinely portable lab-on-a-chip devices. The method is exemplified in the fabrication of a closed-loop bidirectional SAW pumping concept with applications in micro-scale flow control, and represents the first demonstration of closed channel SAW pumping in a bonded glass/LiNbO(3) device.     

Phase diagram and structural evolution of Ag-Au bimetallic nanoparticles: molecular dynamics simulations

We studied the structural evolution of a 270-atom Ag-Au bimetallic nanoparticle (2 nm in size) with varying composition and temperature. The liquid to solid transition region and the solid-state structure were investigated using molecular dynamics simulations. To determine the exact transition temperature region, we applied the mean square displacement and structure deviation methods, as well as the generally used caloric curve of potential energy versus temperature. The results showed that a complete solid-solution phase diagram of the binary Ag-Au system was obtained. Irrespective of the composition, the freezing temperature of a Ag-Au bimetallic nanoparticle was lower than that of the bulk state by a margin of several hundred degrees, and three different solid-state structures are proposed in relation to the Au composition. Our phase diagram offers guidance for the application of Ag-Au nanoparticles.     

Light-induced rearrangements of chemisorbed dyes on anatase(101)

Photoinduced molecular rearrangements are important in daily events essential for life such as visual perception and photo-protection of light harvesting complexes in plants. In this study we demonstrate that similar photoarrangements appear in an analogous technological application where the device performance is controlled by chromophores in sensitized anatase TiO(2), one of the main components for light-harvesting in dye-sensitized solar cells (DSC). STM reveals that illumination leads to distortions of organic dyes containing conjugated backbones and of cis-bis(isothiocyanate)-bis-(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II)-bis(tetrabutylammonium), known as N719. The dyes were adsorbed in a closed-packed mode on an anatase(101) single crystal surface and imaged in the dark and under white light illumination in an ultra-high vacuum (UHV). STM images of N719 clearly suggest rearrangements caused by rotation of the dye. Conversely, organic dyes rearrange by photoisomerization depending on the number of double bonds, their position in the molecular structure and on the ligand modifications.     

Uniform mixing in paper-based microfluidic systems using surface acoustic waves

Paper-based microfluidics has recently received considerable interest due to their ease and low cost, making them extremely attractive as point-of-care diagnostic devices. The incorporation of basic fluid actuation and manipulation schemes on paper substrates, however, afford the possibility to extend the functionality of this simple technology to a much wider range of typical lab-on-a-chip operations, given its considerable advantages in terms of cost, size and integrability over conventional microfluidic substrates. We present a convective actuation mechanism in a simple paper-based microfluidic device using surface acoustic waves to drive mixing. Employing a Y-channel structure patterned onto paper, the mixing induced by the 30 MHz acoustic waves is shown to be consistent and rapid, overcoming several limitations associated with its capillary-driven passive mixing counterpart wherein irreproducibilities and nonuniformities are often encountered in the mixing along the channel--capillary-driven passive mixing offers only poor control, is strongly dependent on the paper's texture and fibre alignment, and permits backflow, all due to the scale of the fibres being significant in comparison to the length scales of the features in a microfluidic system. Using a novel hue-based colourimetric technique, the mixing speed and efficiency is compared between the two methods, and used to assess the effects of changing the input power, channel tortuousity and fibre/flow alignment for the acoustically-driven mixing. The hue-based technique offers several advantages over grayscale pixel intensity analysis techniques in facilitating quantification without limitations on the colour contrast of the samples, and can be used, for example, for quantification in on-chip immunochromatographic assays.     

Tetrasubstituted phenanthrolines as highly potent, water-soluble, and selective g-quadruplex ligands

Small molecules capable of stabilizing the G-quadruplex (G4) structure are of interest for the development of improved anticancer drugs. Novel 4,7-diamino-substituted 1,10-phenanthroline-2,9-dicarboxamides that represent hybrid structures of known phenanthroline-based ligands have been designed. An efficient synthetic route to the compounds has been developed and their interactions with various G4 sequences have been evaluated by F?rster resonance energy transfer (FRET) melting assays, fluorescent intercalator displacement (FID), electrospray ionization mass spectrometry (ESI-MS), and circular dichroism (CD) spectroscopy. The preferred compounds have high aqueous solubility and are strong and potent G4 binders with a high selectivity over duplex DNA; thus, they represent a significant improvement over the lead compounds. Two of the compounds are inhibitors of HeLa and HT1080 cell proliferation.     

An efficient method for the preparation of tertiary esters by palladium-catalyzed alkoxycarbonylation of aryl bromides

The palladium-catalyzed alkoxycarbonylation of aryl bromides is described for the efficient preparation of tertiary esters. The protocol proved compatible with a wide variety of functionalized (hetero)aromatic bromides, as well as several different sterically hindered tertiary alcohols, affording the alkoxycarbonylated products in high yields. Finally, the formation of aromatic trityl esters is discussed.     

Visible light driven hydrogen production from a photo-active cathode based on a molecular catalyst and organic dye-sensitized p-type nanostructured NiO

A molecular device with a photocathode for hydrogen generation has been successfully demonstrated, based on an earth abundant and inexpensive p-type semiconductor NiO, an organic dye P1 and a cobalt catalyst Co1.     

Rational engineering of Candida antarctica lipase B for selective monoacylation of diols

The enzyme Candida antarctica lipase B was subjected to site directed mutagenesis suggested by molecular modelling. The selectivity for the enzyme increased towards a range of diols over their corresponding monoesters as an effect of the mutations.     

Peculiarities of crystal structures and magnetic properties of Cu(II) and Ni(II) mixed-ligand complexes on the 1,3-dithiole-2-thione-4,5-dithiolate basis

Mixed-ligand Cu(II) and Ni(II) complexes, [Cu(dmit)(bpy)]₂ (I), [Ni(dmit)(phen)₂] (II) and [Ni(dmit)(phen)₂]·CH₂Cl₂ (III) (dmit=1.3-dithiole-2-thione-4.5-dithiolate, phen=1.10-phenantroline, bpy=2.2′-bipyridine) have been prepared by ligand exchange between phen or bpy and (Bu₄N)₂[M(dmit)₂] (M=Ni, Cu) and characterized by elemental analysis, IR spectroscopy, single-crystal X-ray analysis and by investigation of magnetic and resonance properties. In complex I, the monomeric units form dimers in a head-to-tail arrangement by weak coordination bonds between copper and dithiolate sulfur atoms and π–π interactions between dmit and bpy from neighboring monomers. Dimers in I are further extended into chains by weak Cu–S(thione) contacts. In crystal packing of complex II and III, there exists a weak π–π interaction between two parallel phen molecules of the adjacent complexes. As a consequence, the magnetic and resonance characteristics of copper complex may be described in approximation of exchange-coupled pairs of Cu²⁺ ions with ion spin S=1/2. The nickel complexes are described by isotropic exchange model for single-site spin S=1.     

Supercharacters,symmetric functions in noncommuting variables,and related Hopf algebras

We identify two seemingly disparate structures: supercharacters, a useful way of doing Fourier analysis on the group of unipotent uppertriangular matrices with coefficients in a finite field, and the ring of symmetric functions in noncommuting variables. Each is a Hopf algebra and the two are isomorphic as such. This allows developments in each to be transferred. The identification suggests a rich class of examples for the emerging field of combinatorial Hopf algebras.